Tag: surface temperature

Our Solar System is a fascinating place. Between its eight planets and many dwarf planets, there are some serious differences in terms of orbit, composition, and temperature. Whereas conditions within the inner Solar System, where planets are terrestrial in nature, can get pretty hot, planets that orbit beyond the Frost Line – where it is cold enough that volatiles (i.e. water, ammonia, methane, CO and CO²) condense into solids – can get mighty cold!

It is in this environment that we find Neptune, the Solar System’s most distance (and hence most cold) planet. While this gas/ice giant has no “surface” to speak of, Earth-based research and flybys have been conducted that have managed to obtain accurate measurements of the temperature in the planet’s upper atmosphere. All told, the planet experiences temperatures that range from approximately 55 K (-218 °C; -360 °F) to 72 K (-200 °C; -328 °F), making it the coldest planet in the Solar System.

Orbital Characteristics:

Of all the planets in the Solar System, Neptune orbits the Sun at the greatest average distance. With a very minor eccentricity (0.0086), it orbits the Sun at an semi-major axis of approximately 30.11 AU (4,504,450,000,000 km), ranging from 29.81 AU (4.459 x 109 km) at perihelion and 30.33 AU (4.537 x 109 km) at aphelion.

Neptune and the icy-asteroid-rich Kuiper Belt that lies beyond its orbit. Credit: NASA

Neptune takes 16 hours 6 minutes and 36 seconds (0.6713 days) to complete a single sidereal rotation, and 164.8 Earth years to complete a single orbit around the Sun. This means that a single day lasts 67% as long on Neptune, whereas a year is the equivalent of approximately 60,190 Earth days (or 89,666 Neptunian days).

Because Neptune’s axial tilt (28.32°) is similar to that of Earth (~23°) and Mars (~25°), the planet experiences similar seasonal changes. Combined with its long orbital period, this means that the seasons last for forty Earth years. In addition, the planets axial tilt also leads to variations in the length of its day, as well as variations in temperature between the northern and southern hemispheres (see below).

“Surface” Temperature:

Due to their composition, determining a surface temperature on gas or ice giants (compared to terrestrial planets or moons) is technically impossible. As a result, astronomers have relied on measurements obtained at altitudes where the atmospheric pressure is equal to 1 bar (or 100 kilo Pascals), the equivalent of air pressure here on Earth at sea level.

It is here on Neptune, just below the upper level clouds, that pressures reach between 1 and 5 bars (100 – 500 kPa). It is also at this level that temperatures reach their recorded high of 72 K (-201.15 °C; -330 °F). At this temperature, conditions are suitable for methane to condense, and clouds of ammonia and hydrogen sulfide are thought to form (which is what gives Neptune its characteristically dark cyan coloring).

But as with all gas and ice giants, temperatures vary on Neptune due to depth and pressure. In short, the deeper one goes into Neptune, the hotter it becomes. At its core, Neptune reaches temperatures of up to 7273 K (7000 °C; 12632 °F), which is comparable to the surface of the Sun. The huge temperature differences between Neptune’s center and its surface create huge wind storms, which can reach as high as 2,100 km/hour, making them the fastest in the Solar System.

Temperature Anomalies and Variations:

Whereas Neptune averages the coldest temperatures in the Solar System, a strange anomaly is the planet’s south pole. Here, it is 10 degrees K warmer than the rest of planet. This “hot spot” occurs because Neptune’s south pole is currently exposed to the Sun. As Neptune continues its journey around the Sun, the position of the poles will reverse. Then the northern pole will become the warmer one, and the south pole will cool down.

Neptune’s more varied weather when compared to Uranus is due in part to its higher internal heating, which is particularly perplexing for scientists. Despite the fact that Neptune is located over 50% further from the Sun than Uranus, and receives only 40% its amount of sunlight, the two planets’ surface temperatures are roughly equal.

Four images of Neptune taken a few hours apart by the Hubble Space Telescope on June 25-26, 2011. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

Deeper inside the layers of gas, the temperature rises steadily. This is consistent with Uranus, but oddly enough, the discrepancy is larger. Uranus only radiates 1.1 times as much energy as it receives from the Sun, whereas Neptune radiates about 2.61 times as much. Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. The mechanism for this remains unknown.

And while temperatures on Pluto have been recorded as reaching lower – down to 33 K (-240 °C; -400 °F) – Pluto’s status as a dwarf planet mean that it is no longer in the same class as the others. As such, Neptune remains the coldest planet of the eight.

Earth is the only planet in our Solar System where life is known to exists. Note the use of the word “known”, which is indicative of the fact that our knowledge of the Solar System is still in its infancy, and the search for life continues. However, from all observable indications, Earth is the only place in our Solar System where life can – and does – exist on the surface.

This is due to a number of factors, which include Earth’s position relative to the Sun. Being in the “Goldilocks Zone” (aka. habitable zone), and the existence of an atmosphere (and magnetosphere), Earth is able to maintain a stable average temperature on its surface that allows for the existence of warm, flowing water on its surface, and conditions favorable to life.

Variations:

The average temperature on the surface of Earth depends on a number of factors. These include the time of day, the time of year, and where the temperatures measurements are being taken. Given that the Earth experiences a sidereal rotation of approximately 24 hours – which means one side is never always facing towards the Sun – temperatures rise in the day and drop in the evening, sometimes substantially.

And given that Earth has an inclined axis (approximately 23° towards the Sun’s equator), the Northern and Southern Hemispheres of Earth are either tilted towards or away from the Sun during the summer and winter seasons, respectively. And given that equatorial regions of the Earth are closer to the Sun, and certain parts of the world experience more sunlight and less cloud cover, temperatures range widely across the planet.

However, not every region on the planet experiences four seasons. At the equator, the temperature is on average higher and the region does not experience cold and hot seasons in the same way the Northern and Southern Hemispheres do. This is because the amount of sunlight the reaches the equator changes very little, although the temperatures do vary somewhat during the rainy season.

Measurement:

The average surface temperature on Earth is approximately 14°C; but as already noted, this varies. For instance, the hottest temperature ever recorded on Earth was 70.7°C (159°F), which was taken in the Lut Desert of Iran. These measurements were part of a global temperature survey conducted by scientists at NASA’s Earth Observatory during the summers of 2003 to 2009. For five of the seven years surveyed (2004, 2005, 2006, 2007, and 2009) the Lut Desert was the hottest spot on Earth.

However, it was not the hottest spot for every single year in the survey. In 2003, the satellites recorded a temperature of 69.3°C (156.7°F) – the second highest in the seven-year analysis – in the shrublands of Queensland, Australia. And in 2008, the Flaming Mountain got its due, with a yearly maximum temperature of 66.8°C (152.2°F) recorded in the nearby Turpan Basin in western China.

Meanwhile, the coldest temperature ever recorded on Earth was measured at the Soviet Vostok Station on the Antarctic Plateau. Using ground-based measurements, the temperature reached a historic low of -89.2°C (-129°F) on July 21st, 1983. Analysis of satellite data indicated a probable temperature of around -93.2 °C (-135.8 °F; 180.0 K), also in Antarctica, on August 10th, 2010. However, this reading was not confirmed by ground measurements, and thus the previous record remains.

All of these measurements were based on temperature readings that were performed in accordance with the World Meteorological Organization standard. By these regulations, air temperature is measured out of direct sunlight – because the materials in and around the thermometer can absorb radiation and affect the sensing of heat – and thermometers are to be situated 1.2 to 2 meters off the ground.

Comparison to Other Planets:

Despite variations in temperature according to time of day, season, and location, Earth’s temperatures are remarkably stable compared to other planets in the Solar System. For instance, on Mercury, temperatures range from molten hot to extremely cold, due to its proximity to the Sun, lack of an atmosphere, and its slow rotation. In short, temperatures can reach up to 465 °C on the side facing the Sun, and drop to -184°C on the side facing away from it.

Venus, thanks to its thick atmosphere of carbon dioxide and sulfur dioxide, is the hottest planet in our Solar System. At its hottest, it can reach temperatures of up to 460 °C on a regular basis. Meanwhile, Mars’ average surface temperature is -55 °C, but the Red Planet also experiences some variability, with temperatures ranging as high as 20 °C at the equator during midday, to as low as -153 °C at the poles.

On average though, it is much colder than Earth, being just on the outer edge of the habitable zone, and because of its thin atmosphere – which is not sufficient to retain heat. In addition, its surface temperature can vary by as much as 20 °C due to Mars’ eccentric orbit around the Sun (meaning that it is closer to the Sun at certain points in its orbit than at others).

Since Jupiter is a gas giant, and has no solid surface, an accurate assessment of it’s “surface temperature” is impossible. But measurements taken from the top of Jupiter’s clouds indicate a temperature of approximately -145°C. Similarly, Saturn is a rather cold gas giant planet, with an average temperature of -178 °Celsius. But because of Saturn’s tilt, the southern and northern hemispheres are heated differently, causing seasonal temperature variation.

Uranus is the coldest planet in our Solar System, with a lowest recorded temperature of -224°C, while temperatures in Neptune’s upper atmosphere reach as low as -218°C. In short, the Solar System runs the gambit from extreme cold to extreme hot, with plenty of variance and only a few places that are temperate enough to sustain life. And of all of those, it is only planet Earth that seems to strike the careful balance required to sustain it perpetually.

Variations Throughout History:

Estimates on the average surface temperature of Earth are somewhat limited due to the fact that temperatures have only been recorded for the past two hundred years. Thus, throughout history the recorded highs and lows have varied considerably. An extreme example of this would during the early history of the Solar System, some 3.75 billion years ago.

At this time, the Sun roughly 25% fainter than it is today, and Earth’s atmosphere was still in the process of formation. Nevertheless, according to some research, it is believed that the Earth’s primordial atmosphere – due to its concentrations of methane and carbon dioxide – could have sustained surface temperatures above freezing.

The Earth has been through five major ice ages in the past 2.4 billion years, including the one we are currently living in. Credit: NASA Goddard’s Scientific Visualization Studio

Earth has also undergone periodic climate shifts in the past 2.4 billion years, including five major ice ages – known as the Huronian, Cryogenian, Andean-Saharan, Karoo, and Pliocene-Quaternary, respectively. These consisted of glacial periods where the accumulation of snow and ice increased the surface albedo, more of the Sun’s energy was reflected into space, and the planet maintained a lower atmospheric and average surface temperature.

These periods were separated by “inter-glacial periods”, where increases in greenhouse gases – such as those released by volcanic activity – increased the global temperature and produced a thaw. This process, which is also known as “global warming”, has become a source of controversy during the modern age, where human agency has become a dominant factor in climate change. Hence why some geologists use the term “Anthropocene” to refer to this period.

Internal Temperatures:

When talking about the temperatures of planets, there is a major difference between what is measured at the surface and what conditions exist within the planet’s interior. Essentially, the temperature gets cooler the farther one ventures from the core, which is due to the planet’s internal pressure steadily decreasing the father out one goes. And while scientists have never sent a probe to our planet’s core to obtain accurate measurements, various estimates have been made.

For instance, it is believed that the temperature of the Earth’s inner core is as high as 7000 °C, whereas the outer core is thought to be between 4000 and 6000 °C. Meanwhile, the mantle, the region that lies just below the Earth’s outer crust, is estimated to be around 870 °C. And of course, the temperature continues to steadily cool as you rise in the atmosphere.

In the end, temperatures vary considerably on every planet in our Solar System, due to a multitude of factors. But from what we can tell, Earth is alone in that it experiences temperature variations small enough to achieve a degree of stability. Basically, it is the only place we know of that it is both warm enough and cool enough to support life. Everywhere else is just too extreme!

Venus is often referred to as our “sister planet,” due to the many geophysical similarities that exist between it Earth. For starters, our two planets are close in mass, with Venus weighing in at 4.868 x 1024 kg compared to Earth’s 5.9736×1024 kg. In terms of size, the planets are almost identical, with Venus measuring 12,100 km in diameter and Earth 12,742 km.

In terms of density and gravity, the two are neck and neck – with Venus boasting 86.6% of the former and 90.7% of the latter. Venus also has a thick atmosphere, much like our own, and it is believed that both planets share a common origin, forming at the same time out of a condensing clouds of dust particles around 4.5 billion years ago.

However, for all the characteristics these two planets have in common, average temperature is not one of them. Whereas the Earth has an average surface temperature of 14 degrees Celsius, the average temperature of Venus is 460 degrees Celsius. That is roughly 410 degrees hotter than the hottest deserts on our planet.

In fact, at a searing 750 K (477 °C), the surface of Venus is the hottest in the solar system. Venus is closer to the Sun by 108 million km, (about 30% closer than the Earth), but it is mainly due to the planet’s thick atmosphere. Unlike Earth’s, which is composed primarily of nitrogen, oxygen and ozone, Venus’ atmosphere is an incredibly dense cloud of carbon dioxide and sulfur dioxide gas.

The combination of these gases in high concentrations causes a catastrophic greenhouse effect that traps incident sunlight and prevents it from radiating into space. This results in an estimated surface temperature boost of 475 K (201.85 °C), leaving the surface a molten, charred mess that nothing (that we know of) can live on. Atmospheric pressure also plays a role, being 91 times that of what it is here on Earth; and clouds of toxic vapor constantly rain sulfuric acid on the surface.

In addition, the surface temperature on Venus does not vary like it does here on Earth. On our planet, temperatures vary wildly due to the time of year and even more so based on the location on our planet. The hottest temperature ever recorded on Earth was 70.7°C in the Lut Desert of Iran in 2005. On the other end of the spectrum, the coldest temperature ever recorded on Earth was in Vostok, Antarctica at -89.2 C.

But on Venus, the surface temperature is 460 degrees Celsius, day or night, at the poles or at the equator. Beyond its thick atmosphere, Venus’ axial tilt (aka. obliquity) plays a role in this temperature consistency. Earth’s axis is tilted 23.4 ° in relation to the Sun, whereas Venus’ is only tilted by 3 °.

The only respite from the heat on Venus is to be found around 50 km into the atmosphere. It is at that point that temperatures and atmospheric pressure are equal to that of Earth’s. It is for this reason that some scientists believe that floating habitats could be constructed here, using Venus’ thick clouds to buoy the habitats high above the surface. Additionally, in 2014, a group of mission planners from NASA Langely came up with a mission to Venus’ atmosphere using airships.

These habitats could play an important role in the terraforming of Venus as well, acting as scientific research stations that could either fire off the excess atmosphere off into space, or introduce bacteria or chemicals that could convert all the CO2 and SO2 into a hospitable, breathable atmosphere.

Beyond the fact that it is a hot and hellish landscape, very little is known about Venus’ surface environment. This is due to the thick atmosphere, which has made visual observation impossible. The sulfuric acid is also problematic since clouds composed of it are highly reflective of visible light, which prevents optical observation. Probes have been sent to the surface in the past, but the volatile and corrosive environment means that anything that lands there can only survive for a few hours.

What little we know about the planet’s surface has come from years worth of radar imaging, the most recent of which was conducted by NASA’s Magellan spacecraft (aka. the Venus Radar Mapper). Using synthetic aperture radar, the robotic space probe spent four years (1990-1994) mapping the surface of Venus and measuring its gravitational field before its orbit decayed and it was “disposed of” in the planet’s atmosphere.

The images provided by this and other missions revealed a surface dominated by volcanoes. There are at least 1,000 volcanoes or volcanic centers larger than 20 km in diameter on Venus’ harsh landscape. Many scientists believe Venus was resurfaced by volcanic activity 300 to 500 million years ago. Lava flows are a testament to this, which appear to have produced channels of hardened magma that extend for hundreds of km in all directions. The mixture of volcanic ash and the sulfuric acid clouds is also known to produce intense lightning and thunder storms.

The temperature of Venus is not the only extreme on the planet. The atmosphere is constantly churned by hurricane force winds reaching 360 kph. Add to that the crushing air pressure and rainstorms of sulfuric acid, and it becomes easy to see why Venus is such a barren, lifeless rock that has been hard to explore.

As you probably realize, that number is just an average. The Earth’s temperature can be much higher or lower than this temperature. In the hottest places of the planet, in the deserts near the equator, the temperature on Earth can get as high as 57.7° C. And then in the coldest place, at the south pole in Antarctica, the temperature can dip down to -89° C.

The reason the average temperature on Earth is so high is because of the atmosphere. This acts like a blanket, trapping infrared radiation close to the planet and warming it up. Without the atmosphere, the temperature on Earth would be more like the Moon, which rises to 116° C in the day, and then dips down to -173° C at night.

Jupiter, which takes its name from the father of the gods in ancient Roman mythology, is the largest planet in our Solar System. It also has the most moon’s of any solar planet – with 50 accounted for and another 17 awaiting confirmation. It has the most intense surface activity, with storms up to 600 km/h occurring in certain areas, and a persistent anticyclonic storm that is even larger than planet Earth.

And when it comes to temperature, Jupiter maintains this reputation for extremity, ranging from extreme cold to extreme hot. But since the planet has no surface to speak of, being a gas giant, it’s temperature cannot be accurately measured in one place – and varies greatly between its upper atmosphere and core.

Currently, scientists do not have exact numbers for the what temperatures are like within the planet, and measuring closer to the interior is difficult, given the extreme pressure of the planet’s atmosphere. However, scientists have obtained readings on what the temperature is at the upper edge of the cloud cover: approximately -145 degrees C.

Because of this extremely cold temperature, the atmosphere at this level is composed primarily of ammonia crystals and possibly ammonium hydrosulfide – another crystallized solid that can only exist where conditions are cold enough.

However, if one were to descend a little deeper into the atmosphere, the pressure would increases to a point where it is ten times what it is here on Earth. At this altitude, the temperature is thought to increase to a comfortable 21 °C, the equivalent to what we call “room temperature” here on Earth.

Descend further and the hydrogen in the atmosphere becomes hot enough to turn into a liquid and the temperature is thought to be over 9,700 C. Meanwhile, at the core of the planet, which is believed to be composed of rock and even metallic hydrogen, the temperature may reach as high as 35,700°C – hotter than even the surface of the Sun.

Interestingly enough, it may be this very temperature differential that leads to the intense storms that have been observed on Jupiter. Here on Earth, storms are generated by cool air mixing with warm air. Scientists believe the same holds true on Jupiter.

A close-up of Jupiter’s great red spot, an anticyclonic storm that is larger than Earth. Credit: NASA/JPL-Caltech/ Space Science Institute

One difference is that the jet streams that drive storms and winds on Earth are caused by the Sun heating the atmosphere. On Jupiter it seems that the jet streams are driven by the planets’ own heat, which are the result of its intense atmospheric pressure and gravity.

During its orbit around the planet, the Galileo spacecraft observed winds in excess of 600 kph using a probe it deployed into the upper atmosphere. However, even at a distance, Jupiter’s massive storms can be seen to be humungous in nature, with some having been observed to grow to more than 2000 km in diameter in a single day.

And by far, the greatest of Jupiter’s storms is known as the Great Red Spot, a persistent anticyclonic storm that has been raging for hundreds of years. At 24–40,000 km in diameter and 12–14,000 km in height, it is the largest storm in our Solar System. In fact, it is so big that Earth could fit inside it four to seven times over.

Given its size, internal heat, pressure, and the prevalence of hydrogen in its composition, there are some who wonder if Jupiter could collapse under its own mass and trigger a fusion reaction, becoming a second star in our Solar System. There are a few reasons why this has not happened, much to the chagrin of science fiction fans everywhere!

This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen. Credit: Kelvinsong/Wikimedia Commons

For starters, despite its mass, gravity and the intense heat it is believed to generate near its core, Jupiter is not nearly massive or hot enough to trigger a nuclear reaction. In terms of the former, Jupiter would have to multiply its current mass by a factor of 80 in order to become massive enough to ignite a fusion reaction.

With that amount of mass, Jupiter would experience what is known as gravitational compression (i.e. it would collapse in on itself) and become hot enough to fuse hydrogen into helium. That is not going to happen any time soon since, outside of the Sun, there isn’t even that much available mass in our Solar System.

Of course, others have expressed concern about the planet being “ignited” by a meteorite or a probe crashing into it – as the Galileo probe was back in 2003. Here too, the right conditions simply don’t exist (mercifully) for Jupiter to become a massive fireball.

While hydrogen is combustible, Jupiter’s atmosphere could not be set aflame without sufficient oxygen for it to burn in. Since no oxygen exists in the atmosphere, there is no chance of igniting the hydrogen, accidentally or otherwise, and turning the planet into a tiny star.

Scientists are striving to better understand the temperature of Jupiter in hopes that they will eventually be able to understand the planet itself. The Galileo probe helped and data from New Horizons went even further. NASA and other space agencies are planning future missions that should bring new data to light.